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Regular milk contains the milk sugar lactose, while lactose-free milk does not. Lactase, an enzyme produced by the stomach, breaks down the milk sugar galactose so you can absorb it. People who have lactose intolerance, a lactase deficiency, have gastrointestinal symptoms when they consume dairy products containing lactose. Commercial milk producers add lactase to lactose-free milk so that you can drink it without experiencing gastrointestinal symptoms. Lactase makes the milk taste sweeter. To render the lactase enzyme inactive, manufacturers ultra-pasteurize the milk, which can change the consistency and taste. Ultra-pasteurization also extends the shelf life.

Taste Differences

Lactose-free milk tastes sweeter than regular milk because the milk sugar lactase is broken down into two simple sugars, galactose and glucose. Simple sugars taste sweeter on your tongue than complex sugars. A Kansas State University study published in the June 2009 issue of "LWT Food Science and Technology" on the characteristics of lactose-free milk reported that the sweeter, more highly processed, cooked taste of lactose-free milk might be a deterrent to consumer interest in the product.

Shelf Life

Ultra-pasteurized milk has a longer shelf life than regular milk, lasting up to 60 days compared with between seven and 16 days for regular milk, according to Strauss Family Creamery. This is a benefit for the manufacturer because lactose-free milk doesn't have as rapid a turnover on the store shelves, since there isn't as high a demand for it as for regular milk. Producers heat the milk to at least 280 degree Fahrenheit for at least two seconds. Regular pasteurized milk is heated to 170 degrees Fahrenheit for 19 seconds and then immediately cooled to 40 degree Fahrenheit or lower.

Health Benefits

Drinking lactose-free milk can prevent the symptoms of lactose intolerance if you're one of the approximately 30 million Americans with lactose intolerance, according to MedlinePlus. The most common symptoms include abdominal discomfort, including nausea, diarrhea, gas and bloating, which begin 30 minutes to two hours after ingesting lactose. The incidence of lactose intolerance increases as you get older; it occurs most commonly in people of African-American, Asian, Mediterranean or Native American descent. Some people can tolerate a small amount of lactose in their diet, while others can't. Lactose intolerance doesn't cause serious illness or have long-term health effects. Avoiding lactose or taking over-the-counter lactase when you eat dairy products is the only treatment necessary.

Nondairy Lactose-Free Milks

Some beverages that advertise themselves as lactose free milk don't contain any cow's milk. Instead, manufacturers use soybeans, rice, almonds or other foods to produce a fluid that they call milk. This type of lactose-free milk does not have the same benefits of cow's milk, such as high calcium content. In some cases, manufacturers add vitamin D and calcium to this type of milk to produce a beverage similar in nutrition to milk but without any lactose risks.

About the Author

A registered nurse with more than 25 years of experience in oncology, labor/delivery, neonatal intensive care, infertility and ophthalmology, Sharon Perkins has also coauthored and edited numerous health books for the Wiley "Dummies" series. Perkins also has extensive experience working in home health with medically fragile pediatric patients.